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Warming oceans force fish south

TANYA NOLAN: New research shows the world's warming oceans are forcing tropical fish to move south and putting other habitats at risk.

While up north they help protect coral reefs, down south they attack and destroy underwater forests, which support a range of species, and researchers say the migration is also threatening Australia's lobster industry.

The ABC's environment and science reporter Jake Sturmer has the story.

(Excerpt from Finding Nemo movie trailer)

MARLIN: I've got to find my son Nemo.

TURTLE: Rap shell dude.

MARLIN: What?

VOICEOVER: To find Nemo…

DORY: Let's ask for directions?

MARLIN: No!

DORY: What is it with men asking for directions?

VOICEOVER: …will take a miracle.

(End of excerpt)

JAKE STURMER: The Hollywood blockbuster Finding Nemo charts the story of a tropical fish abducted from the Great Barrier Reef that ends up in Sydney Harbour.

Animated fantasy supposedly, but now researchers are finding more and more tropical species down south thanks to the warming oceans.

University of New South Wales researcher Dr Adriana Verges has been studying their movements closely.

Her work has been published in the journal Proceedings of the Royal Society B.

ADRIANA VERGES: Tropical fish from places like, say, the Great Barrier Reef are moving into temperate regions, for example places like Sydney. We're starting to see more and more tropical fishes, especially at the end of the summer.

JAKE STURMER: That's because the flow of the East Australian Current has increased, warming the waters of Australia's south-east at two to three times the global average.

Dr Verges says it's because of climate change.

ADRIANA VERGES: Tropical species that perhaps were carried by this current, you know, they used to die once they hit certain cold temperatures but because the temperatures are now warmer overall, especially in the winter, species are starting to stay and form populations.

JAKE STURMER: Tropical fish around coral reefs are a good thing. They keep the reefs free of seaweed and allow the coral to flourish.

But in temperate waters, they destroy underwater kelp forests.

What's the problem with the fish eating the kelp forests?

ADRIANA VERGES: Well, once the underwater forests disappear, all the species that depend on them also go. So for example this has been well documented in Japan where the loss of algal forests has lead to the collapse of entire fisheries like the abalone fishery for example.

Abalone are associated with kelp. They're only found where there's kelp or other kind of big seaweeds. So if they go, the abalone go. So it has economic implications. Other species that depend on kelp that we like to eat are lobster, for example, and then a whole host of fish.

JAKE STURMER: So this could be a threat to the lobster industry?

ADRIANA VERGES: Yeah absolutely, absolutely. So in places like Japan for example, it's actually the fisherman that are trying to fight to restore the kelp in places where it's disappeared, it's that big a deal for the fisherman themselves.

JAKE STURMER: Is there a fix? Is there any way to stop this?

ADRIANA VERGES: Well, we should definitely try and stop CO2 emissions. Any efforts to stop climate change are going to be key in at least slowing down this process.

Other than that, what can be done is changing some of our management practices. So perhaps shifting the species that we fish for, so for example in certain areas targeting fisheries towards this plant-eating herbivorous fish. That would be a good thing.

TANYA NOLAN: University of New South Wales researcher Dr Adriana Verges ending that report from Jake Sturmer.